Liquid crystal display devices, which are thin, light display devices, are employed not only as display screens for computers but are also employed for television sets and for projectors, and new applications for the devices are constantly being found. For a liquid crystal display device, a liquid crystal solution is sealed between two glass substrates, and by applying predetermined voltages to the liquid crystals for respective pixels, the relative brightness of the display can be adjusted in accordance with the alignment of the liquid crystals. A thin film transistor, shaped as a matrix, is formed on one of the glass substrates and is employed as a switching device that, in conjunction with a voltage driver that generates desired voltages and places them on a data line that is connected to the switching device, applies the predetermined voltages to the liquid crystals.
In the manufacture of the thus structured liquid crystal display devices, the most important testing procedure is the one for testing the electrical connections of a circuit. If one electrical connection failure is found in a driver for a liquid crystal display device, it is regarded as a line defect, and that display device is judged defective. The testing procedure is performed to find such defective units. Generally, in the testing procedure, an electrical circuit is actually electrified to display an image and the quality of the image is examined visually. In another type of testing procedure, the electrical connections of the circuit are examined without actually outputting an image. In either testing procedure, it is necessary to conduct electricity to a circuit formed on a glass substrate (hereinafter referred to as a test object) that is to be inspected.
A tool used for electrification in the test process is a prober. According to a common method used for conducting electricity, a prober is brought into contact with a conductive contact point (hereinafter referred to as a pad) on a test object, and electricity is conducted thereto. The probing technique was originally developed for testing semiconductor devices, and the original prober is a so-called pin prober, for which an extremely fine line is employed as a conductive member, its distal end being used to contact a test pad. The pin prober method of continuity testing has various shortcomings.
As the first of the shortcomings, because of the increased density of integrated circuits manufactured now, the spacing between pins on such probers is extremely small to accommodate the extremely small spacing between pads of the test object. In addition, the diameter of pins on such probers has been drastically reduced. Currently, the pitch between the pads are 70 .mu.m or less. Since a prober having a tiny diameter that corresponds to such a pitch is easily deformed, its service life is short. If the prober is not deformed, adjacent pins may contact each other, which increases the chance that testing will not be performed as expected. In addition, because of the fine structure, it is very difficult to accurately bring the pin prober into contact with a test pad. While constant pressure must be applied to bring the prober into contact with the contact point, the applied pressure must be extremely light because of the tiny diameter of the prober. However, when too light a pressure is applied, it is more difficult for the prober to penetrate an oxide film on the surface of a contact point so that electrical contact can be made between the distal end of the prober and the pad surface.
A probe block may be used to accurately bring the prober into contact with a test pad in accordance with the position pattern of the test pad. Because of the fine circuit pattern, a high degree of accuracy and material durability are required to manufacture probe blocks. This prolongs the time required to manufacture probe blocks and increases manufacturing costs.
When there is a shift in the positioning of a fine prober, electrical contact cannot be made, and some damage may occur. The lengthening of the time period for manufacturing such test tools, and increase in the manufacturing costs is not compatible with the current trend towards manufacturing a greater variety of product types in smaller quantities than was once the norm.
To cope with the above--noted problems, lately, improved probers have been proposed for replacing the conventional pin probers. As examples there is proposed a prober where the distal end of a lead is specially processed to resemble a pin, a prober where a bump is formed at the distal end of a lead to improve contact, and a prober where the material of the pin prober is improved to provide elasticity. However, the inspiration for these improved probers is basically the same as that which produced the conventional pin prober, and such probers do not adequately address the above shortcomings.
Instead of a pin prober, a flat prober (a plate-like prober) has been proposed as a test tool. For example, Japanese Unexamined Patent Publication No. Hei 7-240443 describes a prober structure wherein test circuitry and a bump that contacts a test object are formed on an insulating substrate in the named order, and the circumference of the bump is covered with an insulating layer. For electrical connection with a pad, the plate-like prober is so designed that a bump that contacts a pad is formed on an organic sheet in accordance with the position pattern of the pad.
However, these existing probers and methods do not describe a method for improving the durability of a conventional plate-like prober, and a method for maintaining satisfactory electrical contact in association with a change in temperature. Further, a plate-like prober currently known has the same problems as does the conventional pin prober relative to accuracy and manufacturing costs. In addition, for a currently known plate-like prober of a type that contacts each TAB of a test object, positioning is required for each TAB and testing costs are increased.
Recently, a technique called COG (Chip On Gate) has become popular. Conventionally, a driver chip of a liquid crystal display device is mounted on a TAB, which is then mounted in a liquid crystal display panel. By the COG technique, however, the driver chip is mounted directly on a liquid crystal panel. Consequently, the width of a test object is narrowed considerably. This makes the pin prober unusable for liquid panel that is fabricated according to the COG technique.